1. Field of the Invention
The invention pertains to the field of variable camshaft timing (VCT) systems. More particularly, the invention pertains to an infinitely variable camshaft indexer with a spool valve and two check valves in the center of the rotor.
2. Description of Related Art
There are many advantages to variable cam timing, such as improving emissions, fuel economy and power density. One method of cam phasing uses a vane type cam phaser or Oil Pressure Actuated device (OPA). The performance of this device is dependent on oil pressure, which is typically a function of engine speed. Therefore, at low speeds (especially when the engine is idle), the Oil Pressure Actuated device has unacceptable performance. A second method of cam phasing, xe2x80x9cCam Torque Actuatedxe2x80x9d (CTA) phasing, captures the cam torsional energy with check valves and recirculates the oil chamber to chamber. Cam Torque Actuated technology works well on I3, V6 and V8 engines because of the amplitude of the cam torques across the speed range. However, Cam Torque Actuated technology does not work as well on 4-cylinder engines across the entire speed range. Therefore, there is a need in the art for technology which works well on 4-cylinder engines.
There have been a number of VCT systems patented in the past.
U.S. Pat. No. 5,386,807 uses torque effects at high speed, and engine pressure at low speed. The control valve is in the phaser core. The phaser has a built-in oil pump to provide oil pressure at low speeds. The oil pump is preferably electromagnetically controlled.
U.S. Pat. No. 6,053,138 discloses a device for hydraulic rotational angle adjustment of a shaft to a drive wheel, especially the camshaft of an internal combustion engine. This device has ribs or vanes that are nonrotatably connected with the shaft. These ribs or vanes are located in the compartments of a compartmented wheel. The compartments of the compartmented wheel and the ribs and/or vanes produce pressure chambers by whose hydraulic pressurization the two structural elements can be rotated relative to one another. In order to reduce undesired rotation when an insufficient adjusting or retaining pressure is present, a common end face of the compartmented wheel and of the ribs and/or vanes works with an annular piston that exerts a releasable clamping action on the parts that are rotatable relative to one another.
A related patent, U.S. Pat. No. 6,085,708, shows a device for changing the relative rotational angle of the camshaft of an internal combustion engine relative to its drive wheel. This device has an inner part connected with ribs or vanes that is located rotationally movably in a compartmented wheel. This driven compartmented wheel has a plurality of compartments distributed around the circumference divided by ribs or vanes into two pressure chambers each. The change in rotational angle is produced by their pressurization. To minimize the influence of overlapping alternating torque influences from the valve drive of the internal combustion engine, a damping structure is integrated into this device to hydraulically damp the change in rotational position.
Consideration of information disclosed by the following U.S. Patents, which are all hereby incorporated by reference, is useful when exploring the background of the present invention.
U.S. Pat. No. 5,002,023 describes a VCT system within the field of the invention in which the system hydraulics includes a pair of oppositely acting hydraulic cylinders with appropriate hydraulic flow elements to selectively transfer hydraulic fluid from one of the cylinders to the other, or vice versa, to thereby advance or retard the circumferential position on of a camshaft relative to a crankshaft. The control system utilizes a control valve in which the exhaustion of hydraulic fluid from one or another of the oppositely acting cylinders is permitted by moving a spool within the valve one way or another from its centered or null position. The movement of the spool occurs in response to an increase or decrease in control hydraulic pressure, PC, on one end of the spool and the relationship between the hydraulic force on such end and an oppositely direct mechanical force on the other end which results from a compression spring that acts thereon.
U.S. Pat. No. 5,107,804 describes an alternate type of VCT system within the field of the invention in which the system hydraulics include a vane having lobes within an enclosed housing which replace the oppositely acting cylinders disclosed by the aforementioned U.S. Pat. No. 5,002,023. The vane is oscillatable with respect to the housing, with appropriate hydraulic flow elements to transfer hydraulic fluid within the housing from one side of a lobe to the other, or vice versa, to thereby oscillate the vane with respect to the housing in one direction or the other, an action which is effective to advance or retard the position of the camshaft relative to the crankshaft. The control system of this VCT system is identical to that divulged in U.S. Pat. No. 5,002,023, using the same type of spool valve responding to the same type of forces acting thereon.
U.S. Pat. Nos. 5,172,659 and 5,184,578 both address the problems of the aforementioned types of VCT systems created by the attempt to balance the hydraulic force exerted against one end of the spool and the mechanical force exerted against the other end. The improved control system disclosed in both U.S. Pat. Nos. 5,172,659 and 5,184,578 utilizes hydraulic force on both ends of the spool. The hydraulic force on one end results from the directly applied hydraulic fluid from the engine oil gallery at full hydraulic pressure, PS. The hydraulic force on the other end of the spool results from a hydraulic cylinder or other force multiplier which acts thereon in response to system hydraulic fluid at reduced pressure, PC, from a PWM solenoid. Because the force at each of the opposed ends of the spool is hydraulic in origin, based on the same hydraulic fluid, changes in pressure or viscosity of the hydraulic fluid will be self-negating, and will not affect the centered or null position of the spool.
In U.S. Pat. No. 5,361,735, a camshaft has a vane secured to an end for non-oscillating rotation. The camshaft also carries a timing belt driven pulley which can rotate with the camshaft but which is oscillatable with respect to the camshaft. The vane has opposed lobes which are received in opposed recesses, respectively, of the pulley. The camshaft tends to change in reaction to torque pulses which it experiences during its normal operation and it is permitted to advance or retard by selectively blocking or permitting the flow of engine oil from the recesses by controlling the position of a spool within a valve body of a control valve in response to a signal from an engine control unit. The spool is urged in a given direction by rotary linear motion translating means which is rotated by an electric motor, preferably of the stepper motor type.
U.S. Pat. No. 5,497,738 shows a control system which eliminates the hydraulic force on one end of a spool resulting from directly applied hydraulic fluid from the engine oil gallery at full hydraulic pressure, PS, utilized by previous embodiments of the VCT system. The force on the other end of the vented spool results from an electromechanical actuator, preferably of the variable force solenoid type, which acts directly upon the vented spool in response to an electronic signal issued from an engine control unit (xe2x80x9cECUxe2x80x9d) which monitors various engine parameters. The Engine Control Unit receives signals from sensors corresponding to camshaft and crankshaft positions and utilizes this information to calculate a relative phase angle. A closed-loop feedback system which corrects for any phase angle error is preferably employed. The use of a variable force solenoid solves the problem of sluggish dynamic response. Such a device can be designed to be as fast as the mechanical response of the spool valve, and certainly much faster than the conventional (fully hydraulic) differential pressure control system. The faster response allows the use of increased closed-loop gain, making the system less sensitive to component tolerances and operating environment.
In all the systems described above, the controls for camshaft timing are located in the camshaft itself, or downstream of the camshaft, increasing the likelihood for leakage as the hydraulic fluid moves from the spool valve into the vanes of the rotor. Therefore, there is a need in the art for an infinitely variable VCT multi-position cam indexer which decreases leakage during operation.
The present invention is an infinitely variable camshaft timing device (phaser) with a control valve located in the rotor. Since the control valve is in the rotor, the camshaft need only provide a single passage for supplying engine oil or hydraulic fluid, and does not need multiple passageways for controlling the phaser, as in the prior art. Two check valves, an advance chamber check valve and a retard chamber check valve, are also located in the rotor. The check valves are located in the control passages for each chamber. The main advantage of putting the check valves in the advance and retard chambers instead of having a single check valve in the supply is to reduce leakage. This design also eliminates high pressure oil flow across the spool valve and improves the response time of the check valve to the torque reversals due to a shorter oil path. In addition, the phaser of the present invention outperforms an oil pressure actuated device and consumes less oil.
The rotor is connected to the camshaft, and the outer housing and gear move relative to the rotor and camshaft. Source oil is supplied through the center of the camshaft. The position of the spool valve determines if the phaser will advance or retard.